1. Field of the Invention
This invention relates in general to cementing casing in a well, and in particular to an apparatus and method for vibrating the casing string to facilitate the flow of cement.
2. Description of the Prior Art
When drilling an oil or gas well, sections of steel pipe, called casing, are screwed together and lowered into the well. The casing may extend to the surface. Optionally, the casing may be supported by a liner hanger at the lower end of a previously installed string of casing. In both cases, a cement shoe will be located on the lower end of the casing. The cement shoe has a float valve. Cement is pumped from the surface down the casing. The cement flows through the cement shoe and back up the annulus surrounding the casing.
It is important to have good bonding between the well formation and the casing. It is also important to have the cement flow through the annulus without leaving any voids. Sometimes to reduce the chance for voids, the operator will stroke the casing up and down several feet while the cement is being pumped down the casing. While this is workable, the casing might become stuck in an upper position. Also, sometimes an operator will rotate the casing when cementing.